This invention relates to a rotating mechanism of a throttle valve for a fuel supply device of an internal combustion engine. More particularly, the invention relates to a rotating mechanism of a throttle valve adapted to operate the throttle valve by the operation of an engaging member to take an engaging position or nonengaging position of a throttle lever having a cam set to open the throttle valve more than the movement of an actuator of a stepping motor or a DC motor for opening the throttle valve in response to the depression of an accelerator without using the actuator even if the stepping motor or the DC motor becomes defective to cause the throttle valve to become impossible to operate. The invention thus allows the vehicle to travel as well as to accelerate the increase in an air amount by opening the throttle valve more than the movement of a stepping motor as an actuator by the cam lever particularly when the vehicle is necessary to be abruptly accelerated in case of racing, thereby preferably accelerating the vehicle.
In a conventional rotating mechanism of a throttle valve for a fuel supply device of an internal combustion engine, when a stepping motor or a DC motor for actuating the throttle valve becomes defective due to the disconnection of wirings or other cause or a control unit in the fuel supply device becomes defective, the throttle valve does not normally operate so that the internal combustion engine stops with the result that a vehicle cannot travel. Further, when a stepping motor is used as an actuator for operating the throttle valve, a reduction gear ratio is increased so as to improve air amount resolving power between steps of the stepping motor. Thus, the response of the stepping motor upon accelerating of the motor is deteriorated, and it becomes impossible to abruptly accelerate the motor.